Atrazine, a triazine herbicide widely used in the United States, contributes to surface-water and groundwater contamination, as can deisopropylatrazine (DIA) and deethylatrazine (DEA), two of its microbial degradation products. Production of DIA and DEA by native bacteria in aquatic sediments has not been investigated thoroughly. We assessed atrazine and production of DIA and DEA over time in coastal aquatic sediments associated with different land uses including creeks from an undeveloped preserve and a suburban development, a golf course drainage ditch, and a contaminated commercial harbor. Sediments were incubated in microcosms, spiked with U-14C-atrazine, extracted, and analyzed for 14C in a liquid scintillation counter. Atrazine, DIA, and DEA also were quantified by gas chromatography–mass spectrometry. The amount of 14C recovered varied at each site as a function of the sediment organic carbon content and decreased significantly over time. Both DEA and DIA were measured primarily in the aqueous phase. Transformation was more extensive to DIA than to DEA. The ratio of DIA to atrazine recovered from the undeveloped preserve was as high as 0.13. In contrast, the golf course had limited biotransformation, and had the greatest atrazine recoveries so atrazine, not DEA and DIA, may have a greater impact at this site.